The present invention relates to a power transmission ring held between a pair of sheaves and a variable diameter pulley assembly using the same.
Heretofore, there have been proposed variable diameter pulley assemblies adapted to vary an effective radius (contact radius) for a belt looped over a pulley. An exemplary pulley assembly of this type has the following configuration, as shown in FIG. 14. A pair of sheaves 100 is each formed with a tapered power transmission surface 101 and is allowed to be axially moved relative to each other with their power transmission surfaces 101 opposed each other. A power transmission ring 102 with a belt B looped over its outer periphery is held between the pair of power transmission surfaces 101 as allowed to be decentered relative to an axis of the sheaves 100. On the other hand, a coned disk spring 103 biases one of the sheaves 100 toward the other sheave 100 (see, for example, Japanese Unexamined Patent Publication No.11 (1999)-30300).
In the variable diameter pulley assembly of this type, the power transmission ring 102 is constructed from a metal, such as an aluminum alloy, or a synthetic resin material. The power transmission ring 102 is formed with tapered raceway surfaces 105 on its lateral sides, the raceway surfaces 105 shaped in conformity with the power transmission surfaces 101.
The conventional variable diameter pulley assembly effects torque transfer between the power transmission surfaces 101 of the sheaves 100 and the raceway surfaces 105 of the power transmission ring 102. During the torque transfer, both the power transmission surfaces 101 and the raceway surfaces 105 are subject to a significantly increased surface pressure because of a small contact area therebetween. Besides, both the surfaces contact each other in a complicated state involving rolling contact for torque transfer and sliding contact produced when the power transmission ring 102 is decentered. Therefore, the metallic power transmission ring 102 is prone to seize on the power transmission surfaces 101. Although less liable to suffer seizure, the power transmission ring 102 of the synthetic resin has a lower strength than the metallic ring. In the event of a breakage, the power transmission ring 102 of the synthetic resin material will be crushed to become unable to transfer torque. This may result in a case where an automobile becomes inoperable if such a variable diameter pulley assembly is employed for driving an auxiliary machine such as an automotive alternator.
In view of the foregoing, it is an object of the invention to provide a power transmission ring and a variable diameter pulley assembly using the same which are less likely to encounter the seizure and capable of accomplishing a desired strength and which are capable of temporarily transferring torque even in the event of a breakage of a plastic portion.
In accordance with the invention for achieving the above object, a power transmission ring comprises:
an outer periphery with a belt looped thereover;
a plastic ring held between first and second power transmission surfaces, each formed on a corresponding lateral surface of first and second sheaves opposed each other, as allowed to be decentered relative to an axis of the first and second sheaves, having first and second tapered raceway surfaces formed on one and the other of lateral surfaces thereof in parallel relation with the first and second power transmission surfaces, respectively, and allowing the first and second raceway surfaces to be contacted by the first and second power transmission surfaces, respectively; and
a metallic ring having first and second tapered surfaces formed on one and the other of lateral surfaces thereof in parallel relation with the first and second raceway surfaces, respectively, and unified with the plastic ring.
The variable diameter pulley assembly of the invention comprises:
first and second sheaves axially relatively movable as presenting first and second power transmission surfaces to each other, the power transmission surfaces each formed on a corresponding lateral surface of the first and second sheaves;
a resilient member for biasing at least one of the sheaves toward the other; and
a power transmission ring including:
an outer periphery with a belt looped thereover;
a plastic ring held between the first and second power transmission surfaces as allowed to be decentered relative to an axis of the first and second sheaves, having first and second tapered raceway surfaces formed on one and the other of lateral surfaces thereof in parallel relation with the first and second power transmission surfaces, respectively, and allowing the first and second raceway surfaces to be contacted by the first and second power transmission surfaces, respectively; and
a metallic ring having first and second tapered surfaces formed on one and the other of lateral surfaces thereof in parallel relation with the first and second raceway surfaces, respectively, and unified with the plastic ring.
According to the power transmission ring and variable diameter pulley assembly of the above configurations, the first and second raceway surfaces are constructed with the plastic ring. Hence, the first and second raceway surfaces of the plastic ring are less likely to seize on the first and second power transmission surfaces of the first and second sheaves. Since the metallic ring is unified with the plastic ring, a desired strength can be accomplished. Furthermore, the first and second tapered surfaces are respectively formed in parallel with the first and second raceway surfaces, so that even in the event of a crush of the plastic ring, the first and second tapered surfaces are allowed to engage the first and second power transmission surfaces, respectively, for temporary torque transfer therebetween.